Methods of operating fuel cell systems with in-block reforming

ABSTRACT

A fuel cell system and corresponding methods are provided. The fuel cell system includes a fuel cell stack configured for in-block reforming, as well as a pre-reformer. The fuel cell stack may include a plurality of fuel cells. The fuel cell stack may also include a fuel supply manifold, a fuel exhaust manifold, an oxidant supply manifold, and an oxidant exhaust manifold. The fuel supply manifold may be configured to receive fuel, and to supply the fuel to the fuel cell stack for in-block reforming. The fuel exhaust manifold may be configured to expel fuel exhaust from the fuel cell stack. The oxidant supply manifold may be configured to receive an oxidant and to supply the oxidant to the fuel cell stack for in-block reforming. The oxidant exhaust manifold may be configured to expel oxidant exhaust from the fuel cell stack.

RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No.15/794,222, entitled Fuel Cell Systems with In-Bock Reforming, filed onOct. 26, 2017, and is incorporated herein by reference.

FIELD

This disclosure generally relates to fuel cell systems and, morespecifically, to fuel cell systems with in-block reforming of fuel andcorresponding methods.

BACKGROUND

A fuel cell stack is an electrochemical system in which a fuel (such ashydrogen) is reacted with an oxidant (such as oxygen) at hightemperature to generate electricity. The fuel cell stack may includemultiple fuel cells where each fuel cell has an anode, a cathode, and anelectrolyte. The fuel cell stack is typically supported by a system ofcomponents such as reformers, heat exchangers, ejectors, combustors,fuel and oxidant sources, and other components. For example, a source ofunreformed fuel may be supplied via a fuel ejector to a fuel cell systemreformer. The reformer may partially or completely reform the fuel usinga steam method, a dry method, or another reforming method to produce areformate that is supplied to anodes of a fuel cell. For example, insteam reforming of natural gas—sometimes referred to as steam methanereforming (SMR)—steam reacts with methane at high temperatures (600°C.-1100° C.) and in the presence of a metal-based catalyst to yieldcarbon monoxide and hydrogen (CH₄+H₂O

CO+3H₂). Steam reforming may also convert higher hydrocarbons by thesame process (C₂H₆+2H₂O

2CO+5H₂), unless those higher hydrocarbons have already been removedfrom the process gas stream by another process (e.g. pre-reforming). Thefuel cell may expel fuel exhaust from the anode and supply the exhaustto either a suction of a fuel ejector or an auxiliary system.

In addition, an oxidant supply provides an oxidant to the cathodes ofthe fuel cell. The fuel cell may expel oxidant exhaust, such as unusedoxidant, from the cathode. To facilitate the reformation of theunreformed fuel, the fuel cell system may provide a heat input to thereformer by supplying the cathode exhaust, or some other hot fluid, tothe reformer. After transferring its heat into the reforming fuel,cathode exhaust may be supplied to an auxiliary system, recycled back tothe cathodes of the fuel cell via an oxidant air ejector, or both.

The temperature of recycled and fresh oxidant supplied to the cathodeswill increase due to heat input as it passes through the fuel cellstack. However, the heat input into the oxidant may be insufficient tomaintain the oxidant in thermal equilibrium as it flows through the fuelcell system. This is due to, for example, the relatively large amount ofheat input needed to support the reformation of the hydrocarbon fuel. Tothermally balance the oxidant as it flows through the fuel cell stack, aheat exchanger may be introduced into the fuel cell system, typicallyupstream of a cathode inlet. The heat exchanger may be supplied withcombustion products to create a reaction that produces heat. Thecombustion products may include fuel exhaust, such as unused fuel, andcathode exhaust. The reaction may occur in the heat exchanger or inanother component such as, e.g., a combustor located upstream of theheat exchanger.

In this configuration, the oxidant typically is maintained in thermalequilibrium as it flows through the fuel cell system during normaloperations. The heat generated within the fuel cell stack, the heattransferred into the fuel in the reformer, the cooling effect of theoxidant mixing at the cathode ejector, and the heat input from a heatexchanger will balance to maintain this thermal equilibrium; in fact, aheat exchanger upstream of the cathode inlet is sized for such apurpose.

One type of fuel cell is the solid oxide fuel cell (SOFC). The basiccomponents of a SOFC may include an anode, a cathode, a solidelectrolyte, and an interconnect. The fuel may be supplied to the anode,and the oxidant may be supplied to the cathode of the fuel cell. At thecathode, electrons ionize the oxidant. The electrolyte may include amaterial that allows the ionized oxidant to pass there through to theanode while simultaneously being impervious to the fluid fuel andoxidant. At the anode, the fuel is combined with the ionized oxidant ina reaction that releases electrons which are conducted back to thecathode through the interconnect. Heat generated from ohmic losses isremoved from the fuel cell by either a fuel (i.e., anode) exhaust or anoxidant (i.e., cathode) exhaust, or heat is radiated to the environment.

The anode of a SOFC may be a mixed cermet comprising nickel and zirconia(such as, e.g., yttria stabilized zirconia (YSZ)) or nickel and ceria(such as, e.g., gadolinia dope ceria (GDC)). Nickel, and othermaterials, may function not only to support the chemical reactionbetween the fuel and the ionized oxidant but may have catalyticproperties which allow the anode to reform a hydrocarbon fuel within thefuel cell. One method of reforming the hydrocarbon fuel is steamreforming of methane (CH₄), an endothermic reaction (Equation 1):CH₄+H₂O→CO+3H₂ΔH°=206.2 kJ/mole  (Equation 1)Alternative methods of reforming are also available. For example, thehydrocarbon fuel may be reformed by carbon dioxide reforming (also knownas dry reforming) (Equation 2):CO₂+CH₄→2H₂+2CO  (Equation 2)

A SOFC may be structured, e.g., as a segment-in-series or in-planeseries arrangement of individual cells. The oxidant is typicallyintroduced at one end of the series of fuel cells via an oxidant inletand flows over the remaining fuel cells until reaching a cathode exhaustoutlet. Each fuel cell transfers heat into the oxidant thereby raisingits temperature. A temperature gradient can develop in the fuel cellwhich increases from the oxidant inlet to the oxidant exhaust outlet.These temperature gradients can cause thermal stresses on the fuel cell,leading to material degradation or failure of fuel cell components. Inaddition, the thermal stresses on the fuel cell can reduce fuel cellperformance. Some fuel cell systems attempt to alleviate these issuewith the use of in-block reforming (IBR), where a portion of the fuel isreformed within the fuel cell stack. However, these systems typicallystill require a reformer as well as a heat exchanger. Thus, there areopportunities for improvements to fuel cell systems configured forinternal block reforming.

SUMMARY

In accordance with some embodiments of the present disclosure, a fuelcell system is provided. The fuel cell system may include a source offuel and a source of oxidant. The fuel cell system also includes a fuelcell stack configured for IBR, an anode ejector, and a pre-reformer. Thefuel cell stack may include a plurality of fuel cells, each fuel cellincluding an anode, a cathode, and an electrolyte. The fuel cells may beSOFCs. The fuel cell stack may also include a fuel supply manifold, afuel exhaust manifold, an oxidant supply manifold, and an oxidantexhaust manifold. The fuel supply manifold may be configured to receivefuel, and to supply the fuel to the anodes of the plurality of fuelcells. The fuel exhaust manifold may be configured to expel fuel exhaustfrom the fuel cell stack. The oxidant supply manifold may be configuredto receive an oxidant and to supply the oxidant to the cathodes of theplurality of fuel cells, and the oxidant exhaust manifold may beconfigured to expel oxidant exhaust from the fuel cell stack.

The anode ejector of the fuel cell system may be configured to receivefuel from a source of fuel, to receive a portion of exhaust from thefuel cell stack, and to supply a stream of fuel that includes at least aportion of one or more of the received fuel and the received portion ofthe exhaust. In some examples, the anode ejector is configured to supplythe stream of fuel based on a recycle ratio of at least 7.5 (i.e.,750%). The recycle ratio is the ratio (by mass) of the amount of thereceived portion of recycled fuel, in this example the fuel exhaust, tothe amount of received fuel that is provided as the stream of fuel. Insome examples, the anode ejector is configured to supply the stream offuel based on a recycle ratio range between 4.5 and 15 (i.e., 450% and1500%). In other examples, the anode ejector is configured to supply thestream of fuel based on a recycle ratio range between 6 and 8 (i.e.,600% and 800%). In some examples, the anode ejector is configured toreceive a portion of fuel exhaust from the fuel cell stack withoutpassing through a heat exchanger.

As mentioned above the fuel cell system may also include a pre-reformer.The pre-reformer can be disposed between an outlet of the anode ejectorand the fuel supply manifold, and may be configured to remove higherhydrocarbons from the stream of fuel received from the anode ejector.The pre-reformer may also be configured to provide the pre-reformed fuelto the fuel supply manifold. In some examples, the pre-reformer suppliesthe pre-reformed fuel directly to the fuel supply manifold. In someexamples, the pre-former can be an adiabatic catalytic converterconfigured to remove the higher hydrocarbons with no heat input otherthan heat from the stream of fuel from the anode ejector.

In some embodiments, the fuel cell system may also include an auxiliaryejector. For example, the auxiliary ejector may be configured to receivea portion of fuel exhaust from the fuel cell stack, and to receiveoxidant exhaust from the oxidant exhaust manifold. In some embodimentsthe fuel cell system also includes a combustor configured to receivefuel exhaust from the fuel cell stack as well as oxidant exhaust fromthe auxiliary ejector. In some embodiments the fuel cell system may alsoinclude a turbine configured to receive exhaust from the combustor.

In some examples, the fuel cell system includes a heat exchanger locatedeither upstream or downstream of the cathode ejector. The heat exchangermay transfer heat from the exhaust of the auxiliary ejector to theoxidant supply. In some examples, the fuel cell system includes no heatexchangers.

In some embodiments, the fuel cell system may include a compressorconfigured to receive oxidant from the oxidant source. In someembodiments, the fuel cell system may also include a cathode ejector,where the cathode ejector may be configured to receive oxidant from thecompressor, receive oxidant exhaust from the oxidant exhaust manifold ofthe fuel cell stack, and supply the received oxidants, in variousproportions, to the oxidant inlet manifold of the fuel cell stack. Insome examples the oxidant exhaust from the cathode ejector is suppliedto the oxidant inlet manifold of the fuel cell stack without passingthrough a heat exchanger.

In accordance with some embodiments of the present disclosure, a solidoxide fuel cell system is provided. The solid oxide fuel cell system mayinclude a solid oxide fuel cell stack configured for IBR that includesat least one solid oxide fuel cell, where each solid oxide fuel cellincludes an anode, a cathode, and an electrolyte.

The solid oxide fuel cell system may also include an anode loop forsupplying fuel and reformate to the anode of each solid oxide fuel cell.The anode loop may include a fuel inlet manifold, a fuel exhaustmanifold, a fuel source, an anode ejector, and a pre-reformer. The fuelinlet manifold may be configured to supply fuel to the anode of eachsolid oxide fuel cell. The fuel exhaust manifold may be configured toreceive fuel exhaust, such as unused fuel or partially depleted reformedfuel, from the anode of each solid oxide fuel cell. The anode ejectormay be configured to receive fuel from the fuel source and from the fuelexhaust manifold, and to supply a stream of fuel that includes at leasta portion of one or more of the received fuels from the fuel source andthe fuel exhaust manifold. In some examples, the anode ejector isconfigured to supply the stream of fuel based on a recycle ratio of atleast 7.5. In some examples, based on the recycle ratio, for example7.5, the anode ejector supplies a stream of fuel that contains less thanapproximately 11% methane. The pre-reformer can be disposed between anoutlet of the anode ejector and the solid oxide fuel cell stack, and maybe configured to remove higher hydrocarbons from the stream of fuelreceived from the anode ejector.

The solid oxide fuel cell system may also include a cathode loop forsupplying oxidant to the cathode of each solid oxide fuel cell. Thecathode loop may include an oxidant inlet manifold, an oxidant exhaustmanifold, and an oxidant source. The oxidant inlet manifold may beconfigured to supply oxidant to the cathode of each solid oxide fuelcell, and the oxidant exhaust manifold may be configured to receiveoxidant exhaust from each cathode of the solid oxide fuel cells.

In some embodiments, the solid oxide fuel cell system includes acompressor configured to receive oxidant from the source of oxidant. Insome examples, the cathode loop may also include a cathode ejector. Thecathode ejector may be configured to receive oxidant from thecompressor, receive oxidant exhaust from the oxidant exhaust manifold ofthe fuel cell stack, and supply the received oxidants, in variousproportions, to the oxidant inlet manifold of the fuel cell stack.

The solid oxide fuel cell system may also include an auxiliary loop forcombusting a portion of the fuel exhaust from the fuel exhaust manifoldand a portion of the oxidant exhaust from the oxidant exhaust manifold.In some examples, the auxiliary loop may include an auxiliary ejectorand a combustor. The auxiliary ejector may be configured to receive aportion of the oxidant exhaust from the oxidant exhaust manifold, toreceive a portion of oxidant from the oxidant source, and to receive aportion of fuel exhaust from the fuel exhaust manifold. The combustormay be configured to receive the exhaust from the auxiliary ejector. Insome embodiments, the solid oxide fuel cell system includes a turbineconfigured to receive the exhaust from the combustor.

In some embodiments, a fuel cell system including a fuel cell block, anout-of-block oxidant flowpath, and an out-of-block fuel flowpath isprovided. The fuel cell block includes a fuel cell stack comprising aplurality of solid oxide fuel cells, each solid oxide fuel cellcomprising an anode, a cathode, and an electrolyte. The fuel cell blockmay also include an in-block fueling flowpath that includes a fuelsupply manifold, a fuel exhaust manifold, and one or more fuelingchannels in fluid communication with the fuel supply manifold and thefuel exhaust manifold, where each anode is exposed to a fuel flowing inone or more of the fueling channels. The fuel cell block may alsoinclude an in-block oxidizing flowpath that includes an oxidant supplymanifold, an oxidant exhaust manifold, and one or more oxidizingchannels in fluid communication with the oxidant supply manifold and theoxidant exhaust manifold, where each cathode is exposed to an oxidantflowing in one or more oxidizing channels.

The out-of-block oxidant flowpath may include a cathode ejector havingan oxidant supply input, an oxidant recycle input, and a combinedoxidant output. For example, the combined oxidant output may provide amixture of oxidant received via the oxidant supply input, and recycledoxidant received via the oxidant recycle input. The out-of-block oxidantflowpath may also include an oxidant supply conduit in fluidcommunication with the cathode ejector oxidant supply input, an oxidantsource in fluid communication with the oxidant supply conduit, anoxidant recycle conduit in fluid communication with the cathode ejectoroxidant recycle input and the in-block oxidizing flowpath oxidantexhaust manifold. The out-of-block flowpath may also include a combinedoxidant supply conduit in fluid communication with the cathode ejectorcombined oxidant output and the in-block oxidizing flowpath oxidantsupply manifold.

The out-of-block fuel flowpath may include an anode ejector having afuel supply input, a fuel recycle input, and a combined fuel output. Forexample, the combined fuel output may provide a combined fuel based onfuel received via the fuel supply input and recycled fuel received viathe fuel recycle input. The out-of-block flowpath may also include afuel supply conduit in fluid communication with the anode ejector fuelsupply input, a source of fuel in fluid communication with the fuelsupply conduit, a fuel recycle conduit in fluid communication with theanode ejector fuel recycle input and the in-block fueling flowpath fuelexhaust manifold, and a combined fuel supply conduit in fluidcommunication with the anode ejector combined fuel output and thein-block fueling flowpath fuel supply manifold.

In some examples, the out-of-block fuel flowpath along with the in-blockfueling flowpath are configured to effect a recycle ratio in the rangeof 6:1 to 8:1 of a mass of fuel flowing into the anode ejector fuelrecycle input to a mass of fuel flowing into the anode ejector fuelsupply input. In other examples, the out-of-block fuel flowpath alongwith the in-block fueling flowpath are configured to effect a recycleratio in the range of 4.5:1 to 15:1 of a mass of fuel flowing into theanode ejector fuel recycle input to a mass of fuel flowing into theanode ejector fuel supply input. In yet other examples, the out-of-blockfuel flowpath along with the in-block fueling flowpath are configured toeffect a recycle ratio of about 7.5:1 of a mass of fuel flowing into theanode ejector fuel recycle input to a mass of fuel flowing into theanode ejector fuel supply input.

In some examples, the out-of-block fuel flowpath along with the in-blockfueling flowpath are configured to effect a weight percent of methane ina fluid flowing into the in-block fueling flowpath fuel supply manifoldof no greater than eleven percent. In some examples, the out-of-blockfuel flowpath along with the in-block fueling flowpath are configured toeffect a weight percent of methane in a fluid flowing into the in-blockfueling flowpath fuel supply manifold in the range of 0 to 11 percent.

In some examples, the fuel cell system includes an out-of-blockauxiliary flowpath that includes an auxiliary ejector having an oxidantsupply input, a fuel exhaust input, an oxidant exhaust input, a recycleinput, and an output. The auxiliary flowpath further includes an oxidantsupply conduit in fluid communication with the auxiliary ejector oxidantsupply input and the oxidant source; a fuel exhaust conduit in fluidcommunication with the auxiliary ejector fuel exhaust input and thein-block fueling flowpath fuel exhaust manifold; an oxidant exhaustconduit in fluid communication with the auxiliary ejector oxidantexhaust input and the in-block oxidizing flowpath oxidant exhaustmanifold; an auxiliary exhaust conduit in fluid communication with theauxiliary ejector output; and a recycle conduit in fluid communicationwith the auxiliary ejector recycle input and the auxiliary exhaustconduit.

In some examples, the auxiliary flowpath includes a combustor. In someexamples, the fuel cell system includes a heat exchanger fortransferring thermal energy between a fluid output of the combustor anda fluid flowing in the combined oxidant supply conduit. In someexamples, the heat exchanger is located between a fluid output of thecombustor and a fluid flowing in the oxidant supply conduit.

In accordance with some embodiments of the present disclosure, a fuelcell system includes a fuel cell stack, configured for IBR, thatincludes multiple compartments (e.g., segments). The fuel cell systemmay also employ multiple anode ejectors and pre-reformers. The fuel cellsystem may also include a source of fuel and a source of oxidant. Thefuel cell system may also include a first anode ejector, a second anodeejector, a first pre-reformer, and a second pre-reformer. The fuel cellstack may include a plurality of fuel cells, each fuel cell including ananode, a cathode, and an electrolyte. The fuel cells may be SOFCs.

Each compartment of the fuel cell stack may include a fuel supplymanifold and a fuel exhaust manifold. One compartment of the fuel cellstack may include an oxidant supply manifold, where another compartmentof the fuel cell stack includes an oxidant exhaust manifold. The fuelsupply manifold of each fuel cell stack may be configured to receivefuel, and to supply the fuel to the anodes of the plurality of fuelcells. The fuel exhaust manifold of each fuel cell stack may beconfigured to expel fuel exhaust from the fuel cell stack. The oxidantsupply manifold of one compartment of the fuel cell stack may beconfigured to receive an oxidant and to supply the oxidant to thecathodes of the plurality of fuel cells, and the oxidant exhaustmanifold of another compartment of the fuel cell stack may be configuredto exhaust the oxidant from the fuel cell stack.

A first anode ejector of the fuel cell system may be configured toreceive fuel from the source of fuel, to receive a portion of fuelexhaust from one compartment of the fuel cell stack, and to supply afirst stream of fuel that includes at least a portion of one or more ofthe received fuel and the received portion of the fuel exhaust. Thefirst stream of fuel may be supplied to, for example, a firstpre-former. In some examples, the first anode ejector is configured toreceive a portion of the fuel exhaust from a compartment of the fuelcell stack without passing through a heat exchanger.

The first pre-reformer can be disposed between an outlet of the firstanode ejector and the fuel supply manifold, and may be configured toremove higher hydrocarbons from the first stream of fuel received fromthe first anode ejector. In some examples, the first pre-former can bean adiabatic catalytic converter configured to remove the higherhydrocarbons with no heat input other than heat from the stream of fuelfrom the first anode ejector.

A second anode ejector of the fuel cell system may be configured toreceive fuel from the source of fuel, to receive a portion of fuelexhaust from another compartment of the fuel cell stack, and to supply asecond stream of fuel that includes at least a portion of one or more ofthe received fuel and the received portion of the fuel exhaust. Thesecond stream of fuel can be supplied to, for example, a secondpre-former. In some examples, the second anode ejector is configured toreceive a portion of the fuel exhaust from the other compartment of thefuel cell stack without passing through a heat exchanger.

The second pre-reformer can be disposed between an outlet of the secondanode ejector and the fuel supply manifold, and may be configured toremove higher hydrocarbons from the second stream of fuel received fromthe second anode ejector. In some examples, the second pre-former can bean adiabatic catalytic converter configured to remove the higherhydrocarbons with no heat input other than heat from the stream of fuelfrom the second anode ejector.

In some examples, the first anode ejector is configured to supply thefirst stream of fuel based on a recycle ratio of at least 7.5. In someexamples, the first anode ejector is configured to supply the firststream of fuel based on a recycle ratio range between 7.5 and 15.Similarly, in some examples, the second anode ejector is configured tosupply the second stream of fuel based on a recycle ratio of at least7.5. In some examples, the second anode ejector is configured to supplythe second stream of fuel based on a recycle ratio range between 7.5 and15.

In some embodiments, the first anode ejector and the second anodeejector are configured to supply the first stream of fuel and the secondstream of fuel at respective recycle ratios such that the first streamof fuel and the second stream of fuel provide a combined fuel thatcontains less than approximately 11% methane. For example, the firstanode ejector may be configured to supply the first steam of fuel basedon a first ratio of the received first portion of exhaust to thereceived fuel, and the second anode ejector may be configured to supplythe second steam of fuel based on a second ratio of the received portionof exhaust to the received fuel. In some examples, each of the firstratio and second ratio can be in the range of 7.5 to 15.

In some embodiments, the fuel cell system may also include an auxiliaryejector. For example, the auxiliary ejector may be configured to receivea portion of fuel exhaust from the fuel cell stack, and to receive theoxidant exhausted from the oxidant exhaust manifold. In some embodimentsthe fuel cell system also includes a combustor configured to receivefuel exhaust from the fuel cell stack as well as oxidant exhausted fromthe auxiliary ejector. In some embodiments the fuel cell system may alsoinclude a turbine configured to receive the exhaust from the combustor.

In some examples, the fuel cell system includes a heat exchanger locatedeither upstream or downstream of the cathode ejector. The heat exchangermay transfer heat from the exhaust of the auxiliary ejector to theoxidant supply. For example, the heat exchanger may be configured toreceive the exhaust of the auxiliary ejector, and to receive oxidantsupplied from the cathode ejector. The heat exchanger can use thentransfer heat from the exhaust of the auxiliary ejector to oxidantsupply, and provide it to the oxidant inlet manifold of the fuel cellstack. Alternatively, the heat exchanger may be configured to receiveoxidant from the source of oxidant, transfer heat from the exhaust ofthe auxiliary ejector to the oxidant, and provide the oxidant to thecathode ejector.

In some examples, a fuel cell system is provided that includes a fuelcell block, an out-of-block oxidant flowpath, a first out-of-block fuelflowpath, and a second out-of-block fuel flowpath. The fuel cell blockmay include a fuel cell stack with a first and a second segment, eachsegment including a plurality of solid oxide fuel cells, each solidoxide fuel cell comprising an anode, a cathode, and an electrolyte. Thefuel cell block may also include a first in-block fueling flowpathincluding a first fuel supply manifold, a first fuel exhaust manifold,and one or more first fueling channels in fluid communication with thefirst fuel supply manifold and the first fuel exhaust manifold, whereeach anode in the first segment is exposed to a fuel flowing in one ormore of the first fueling channels. The fuel cell block may furtherinclude a second in-block fueling flowpath including a second fuelsupply manifold, a second fuel exhaust manifold, and one or more secondfueling channels in fluid communication with the second fuel supplymanifold and the second fuel exhaust manifold, where each anode in thesecond segment is exposed to a fuel flowing in one or more of the secondfueling channels. The fuel cell block may also include an in-blockoxidizing flowpath including an oxidant supply manifold, an oxidantexhaust manifold, and one or more oxidizing channels in fluidcommunication with the oxidant supply manifold and the oxidant exhaustmanifold, where each cathode in the first and second segments is exposedto an oxidant flowing in one or more oxidizing channels.

The out-of-block oxidizing flowpath may include a cathode ejector havingan oxidant supply input, an oxidant recycle input, and a combinedoxidant output. The out-of-block oxidizing flowpath may also include anoxidant supply conduit in fluid communication with the cathode ejectoroxidant supply input, an oxidant source in fluid communication with theoxidant supply conduit, and an oxidant recycle conduit in fluidcommunication with the cathode ejector oxidant recycle input and thein-block oxidizing flowpath oxidant exhaust manifold. The out-of-blockoxidizing flowpath may also include a combined oxidant supply conduit influid communication with the cathode ejector combined oxidant output andthe in-block oxidizing flowpath oxidant supply manifold.

The first out-of-block fuel flowpath may include a first anode ejectorhaving a fuel supply input, a fuel recycle input, and a combined fueloutput. The first out-of-block fuel flowpath may also include a firstfuel supply conduit in fluid communication with the first anode ejectorfuel supply input, a source of fuel in fluid communication with thefirst fuel supply conduit, and a first fuel recycle conduit in fluidcommunication with the first anode ejector fuel recycle input and thesecond in-block fueling flowpath fuel exhaust manifold. The firstout-of-block fuel flowpath may also include a first combined fuel supplyconduit in fluid communication with the first anode ejector combinedfuel output and the first in-block fueling flowpath fuel supplymanifold.

The second out-of-block fuel flowpath may include a second anode ejectorhaving a fuel supply input, a fuel recycle input, and a combined fueloutput. The second out-of-block fuel flowpath may also include a secondfuel supply conduit in fluid communication with the second anode ejectorfuel supply input, a source of fuel in fluid communication with thesecond fuel supply conduit, and a second fuel recycle conduit in fluidcommunication with the second anode ejector fuel recycle input and thefirst in-block fueling flowpath fuel exhaust manifold. The secondout-of-block fuel flowpath may also include a second combined fuelsupply conduit in fluid communication with the second anode ejectorcombined fuel output and the second in-block fueling flowpath fuelsupply manifold.

In some examples, each of the first and second out-of-block fuelflowpaths and the first and second in-block fueling flowpaths areconfigured to effect a recycle ratio in the range of 7.5 to 15 of a massof fuel flowing into the anode ejector fuel recycle input to a mass offuel flowing into the anode ejector fuel supply input.

In some examples, the fuel cell system fuel cell block with a fuel cellstack including a first and a second segment includes an out-of-blockauxiliary flowpath that includes an auxiliary ejector having an oxidantsupply input, a fuel exhaust input, an oxidant exhaust input, a recycleinput, and an output. The auxiliary flowpath may also include an oxidantsupply conduit (e.g., supply line) in fluid communication with theauxiliary ejector oxidant supply input and an oxidant source. Theauxiliary flowpath may also include a fuel exhaust conduit in fluidcommunication with the auxiliary ejector fuel exhaust input and thefirst in-block fueling flowpath fuel exhaust manifold, and an oxidantexhaust conduit in fluid communication with the auxiliary ejectoroxidant exhaust input and the second in-block oxidizing flowpath oxidantexhaust manifold. The auxiliary flowpath may also include an auxiliaryexhaust conduit in fluid communication with the auxiliary ejectoroutput; and a recycle conduit in fluid communication with the auxiliaryejector recycle input and the auxiliary exhaust conduit.

In some examples, a fuel cell system includes a fuel cell stack thatincludes a plurality of solid oxide fuel cells each having an anode, acathode, and an electrolyte. The fuel cell system may also include afuel supply manifold, a fuel exhaust manifold, and one or more fuelingchannels providing a flowpath between the fuel supply and fuel exhaustmanifolds. The one or more fueling channels are in fluid communicationwith the anodes of the plurality of fuel cells. The fuel cell system mayalso include a fueling system that includes a source of unreformed fuel,and an ejector having an input of unreformed fuel from the fuel source,an input of recycle fuel from the fuel exhaust manifold, and an outputof combined fuels from the inputs that is provided to the fuel supplymanifold. Additionally or alternatively, the fuel cell system may beconfigured such that the recycle ratio of the mass of recycle fuel tothe mass of unreformed fuel is in the range of 4.5:1 to 15:1.Additionally or alternatively, the fuel cell system may be configuredsuch that the output of the combined fuels provided to the fuel supplymanifold includes no more than 11% by weight of methane. Additionally,or alternatively, the fuel cell system may be configured such that thetemperature of the fluid entering the fuel supply manifold is no greaterthan the temperature of the combined fuels output from the ejector. Forexample, the fuel cell system may not include a heat exchanger betweenthe output of the ejector and the fuel supply manifold that wouldotherwise provide thermal energy (i.e., heat) to the fuel flowing intothe fuel supply manifold.

Corresponding methods are also contemplated. In some examples, a fuelcell system includes a fuel cell stack configured for in-blockreforming. The method includes receiving, by a fuel supply manifold ofthe fuel cell stack, a fuel from a source of fuel. The method may alsoinclude receiving, by an oxidant supply manifold of the fell cell stack,an oxidant from a source of oxidant. The method may also includereforming, by the fuel cell stack, the received fuel with the receivedoxidant. In some examples, all fuel reforming of the fuel cell system isperformed by the fuel cell stack (i.e., 100% in-block reforming). Themethod may also include expelling, by the fuel cell stack, fuel exhaustfrom the fuel cell stack. The method may also include expelling, by anoxidant exhaust manifold of the fuel cell stack, cathode exhaust, suchas oxidant. The method may also include receiving, by an anode ejector,fuel from the source of fuel, and receiving, by the anode ejector, afirst portion of the fuel exhaust from the fuel exhaust manifold. Themethod may also include supplying, by the anode ejector, a stream offuel that includes at least a portion of one or more of the receivedfuel and the received first portion of the fuel exhaust. The method mayalso include removing, by a pre-reformer, higher hydrocarbons from astream of fuel from the anode ejector; and providing, by thepre-reformer, the stream of fuel to the fuel supply manifold of the fuelcell stack for the in-block reforming.

In another example, a method for providing fuel to the anodes of a solidoxide fuel cell stack includes: drawing unreformed fuel from a fuelsource; combining the unreformed fuel with at least a portion of thefuel exhausted from the fuel cell stack; pre-reforming the combinedunreformed fuel and exhausted fuel; and reforming the unreformed fuel,wherein the improvement comprises reforming all of the unreformed fuelin the fuel cell stack.

In yet another example, a method in a fuel cell system includesexpelling, by a fuel exhaust manifold of a fuel cell stack, fuelexhaust; expelling, by an oxidant exhaust manifold of the fuel cellstack, oxidant exhaust; receiving, by an anode ejector, fuel from asource of fuel; receiving, by the anode ejector, a first portion of thefuel exhaust from the fuel exhaust manifold; supplying, by the anodeejector, a stream of fuel comprising at least a portion of one or moreof the received fuel and the received first portion of the fuel exhaustto a pre-reformer; removing, by the pre-reformer, higher hydrocarbonsfrom the stream of fuel from the anode ejector; providing, by thepre-reformer, the stream of fuel to a fuel supply manifold of the fuelcell stack for in-block reforming; receiving, by an oxidant supplymanifold of the fell cell stack, an oxidant from a source of oxidant;and in-block reforming, by the fuel cell stack, of the stream of fuelwith the received oxidant, wherein all fuel reforming of the fuel cellsystem is performed by the fuel cell stack

In some examples, the anode ejector supplies a stream of fuel includingat least a portion of one or more of the received fuel and the receivedfirst portion of the fuel exhaust to a pre-reformer based on a recycleratio range, such as a range of 7.5 to 15, of a mass of the firstportion of the fuel exhaust from the fuel exhaust manifold to a mass ofthe fuel from the source of fuel. In another example, the anode ejectorsupplies a stream of fuel including at least a portion of one or more ofthe received fuel and the received first portion of the fuel exhaust toa pre-reformer, where a weight percent of methane in the stream of fuelsupplied by the anode ejector is no greater than eleven percent. Othercorresponding methods in accordance with the disclosures herein are alsocontemplated.

Among other advantages, the present disclosures provide for fuel cellsystems that include fuel cell stacks configured for in-block reforming.The fuel cell systems include pre-reformers where incoming fuel ispre-reformed to remove higher hydrocarbons, and the remainder of thefuel is reformed directly in the fuel cell stack without the need for anexternal reformer. In this manner, the difference between the fuel cellstack (cathode) air temperature at the outlet of the fuel cell stack andthe inlet of the fuel cell stack is significantly reduced. As a result,the temperature of the fuel incoming to the fuel cell stack inlet isincreased. In addition, the temperature of the fuel exiting the fuelcell stack is decreased, thus reducing fuel cell stack exit degradation.Another advantage is a more uniform current distribution within the fuelcell stack, resulting in a longer lasting fuel cell stack. For example,the internal electrical resistance of the fuel cell varies withtemperature. As such, the amount of current a fuel cell can delivervaries with temperature. A more uniform temperature throughout the fuelcell stack would mean all cells have a narrower range of internalresistance and therefore would produce a narrower range of currents.This is an advantage at least because the fuel cell stack tends todegrade based on how much current is drawn. If some fuel cells degradefaster than others, the fuel cell stack may reach its end-of-lifecondition although some cells still remain useful. There are also costadvantages to this system, as there is no need for an external reformerin the fuel cell system. Other advantages of the present subject matterwill be readily apparent to one skilled in the art to which thedisclosure pertains from a perusal of the claims, the appended drawings,and the following detail description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a fuel cell system in accordance with someembodiments of the present disclosure;

FIG. 2 illustrates another fuel cell system in accordance with someembodiments of the present disclosure;

FIG. 3 illustrates yet another fuel cell system in accordance with someembodiments of the present disclosure; and

FIG. 4 illustrates yet another fuel cell system in accordance with someembodiments of the present disclosure.

DETAILED DESCRIPTION

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. Theobjectives and advantages of the claimed subject matter will become moreapparent from the following detailed description of the preferredembodiments thereof in connection with the accompanying drawings. Itshould be understood, however, that the present disclosure is notintended to be limited to the particular forms disclosed. Rather, thepresent disclosure is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure asdefined by the appended claims.

FIG. 1 illustrates a fuel cell system 100 that includes a fuel cellstack 102, an oxidant source 108, a fuel source 110, an anode ejector112 (also referred to as a fuel ejector), a cathode ejector 114 (alsoreferred to as an oxidant ejector), a pre-reformer 144, and an auxiliaryejector 116. The system includes IBR of fuel. For example, in someexamples all fuel reforming (i.e., 100%) occurs in the fuel cell stack102. The IBR may include dry or wet reforming. The fuel cell system 100may also include auxiliary equipment and components. In this example,the fuel cell system 100 includes a compressor 134, a turbine 136, agenerator 138, and a recuperator 142.

The fuel cell stack 102 may include a plurality of individual fuel cells(not shown). The individual fuel cells may each comprise an anode, acathode, and an electrolyte. The fuel cell stack 102 may also include afuel supply manifold 120 (also known as a fuel inlet manifold) that isconfigured to receive a stream of fuel from the pre-reformer 144.

The fuel cell stack 102 may also include a fuel exhaust manifold 118configured to expel (e.g., vent) fuel exhaust, inter alia, unused fuel(e.g., fuel that has been reformed (reformate)), fuel cell reactionproducts, or both from the fuel stack 102. The fuel exhaust may besupplied to the suction of the anode ejector 112, suction of theauxiliary ejector 116, or other auxiliary equipment such as, e.g., acombustor (not shown). The fuel exhaust manifold 118 may also beconfigured to expel fuel exhaust to the environment, or may beconfigured to supply or expel the fuel exhaust using any combination ofthese options.

Anode ejector 112 can receive a source of fuel from fuel source 110, andcan also receive fuel exhaust from the fuel exhaust manifold 118 fromfuel cell stack 102 that is recycled back to the anode ejector 112 asmentioned above. The anode ejector 112 is configured to supply the fuelto the pre-reformer 104. In some examples, anode ejector 112 isconfigured to supply fuel based on a high recycle ratio. For example,the anode ejector 112 may be configured to supply fuel based on arecycle ratio in the range of 7.5 to 15. In some examples, the anodeejector 112, based on the recycle ratio it is configured for, suppliesfuel to the pre-reformer with less than 11% methane.

The pre-reformer 144 can be disposed between the outlet of anode ejector112 and the fuel supply manifold 120. The pre-reformer 144 functions toremove higher hydrocarbons from the stream of fuel from the outlet ofthe anode ejector 112, and any higher hydrocarbons that may exist in thefuel exhaust recycled to the anode ejector 112. The pre-reformer 144 maybe an adiabatic catalytic converter capable of removing the higherhydrocarbons with no heat input other than the heat from the fuel fromsource 110 and that recycled from the fuel exhaust 118.

In some examples fuel source 110 provides desulfurized natural gas toanode ejector 112. Methane gas that may exit anode ejector 112 isconverted to synthesis gas in fuel cell stack 102 through steamreforming. The resultant synthesis gas is converted to carbon dioxideand water through the electrochemical process of fuel cell stack 102.

The fuel cell stack 102 may also include an oxidant supply manifold 122(which may be referred to as an oxidant inlet manifold) and an oxidantexhaust manifold 124. The oxidant supply manifold 122 is configured toreceive an oxidant from the cathode ejector 114. The cathode ejector 114is also configured to receive oxidant which is exhausted from theoxidant exhaust manifold 124 of the fuel cell stack 102. The cathodeejector 114 is further configured to provide the received oxidant to theplurality of cathodes in the fuel cell stack 102.

The oxidant exhaust manifold 124 may be configured to exhaust theoxidant from the fuel cell stack 102 for delivery to one or more of thesuction side of cathode ejector 114, the suction side of auxiliaryejector 116, or some other component such as, e.g., a combustor (notshown). The oxidant exhaust manifold 124 may also be configured to ventthe oxidant to the environment, or may be configured to exhaust or ventthe oxidant in any combination of these options.

The oxidant exhaust which is supplied to the suction side of the cathodeejector 114 flows through a portion of a cathode loop. In this example,the cathode loop consists of the flow path of oxidant from the cathodeejector 114 into the oxidant supply manifold 122 from which the oxidantis supplied to the cathodes in the fuel cell stack 102, exhausted outthe oxidant exhaust manifold 124, and back to the suction of the cathodeejector 114. As can be seen, the cathode loop is not a closed systembecause oxidant is allowed to enter the loop from oxidant supply 108 andto exit the loop via the suction of ejector 116. For example, in someembodiments the cathode loop may be considered to include the oxidantsource 108 and the additional components shown between the oxidantsource 108 and the fuel cell stack 102. Additionally, in some examplesthe cathode loop may include a flow of oxidant that is ionized anddiffused through one or more fuel cell electrolytes of fuel cell stack102.

A combustor (not shown), which can be integral to the auxiliary ejector116, can be supplied with fresh oxidant which may provide the energyused to power auxiliary ejector 116. The auxiliary ejector 116 may drawin a portion of fuel exhaust from the fuel exhaust manifold 118, aportion of the oxidant from the oxidant exhaust manifold 124, and mayalso draw in combustion gases produced by auxiliary ejector 116.

In this example, a portion of fuel cell system 100 includes an anodeloop. The anode includes the flow path of fuel from the pre-reformer 144into the fuel inlet manifold 120, out of the fuel exhaust manifold 118,into the anode ejector 112, and back into the pre-reformer 144. Theanode loop may also include the flow path of fuel from fuel source 110into anode ejector 112.

The fuel source 110 may be a source of fuel such as a hydrocarbon fuel,desulfurized natural gas, or any other type of fuel. The oxidant source108 may include storage tanks filled with an oxidant such as, e.g., pureoxygen, atmospheric air, or other oxidant source, or a system designedto generate a supply of oxidant.

As noted above, fuel cell system 100 includes compressor 134, turbine136, generator 138, and recuperator 142. The recuperator 142 can besupplied with oxidant from the compressor 134 for a set of cold-sidechannels therein. Similarly, the recuperator 142 can be supplied withthe exhaust of the turbine 136 to a set of hot-side channels. Therecuperator 142 is upstream of the cathode ejector 114 and the auxiliaryejector 116, and functions to transfer heat between the turbine 136exhaust and the oxidant supplied by the compressor 134.

Generator 138 can supply electrical power to turbine 136. The turbine136 drives the compressor 134 and the generator 138, and can receive thecombustion products from, e.g., auxiliary ejector 116. The combustionproducts may expand as they traverse through the turbine 136. Theturbine 136 exhaust can be supplied to the recuperator 142 to effect aheat transfer therein prior to being exhausted to the atmosphere. Theturbine 136 may also be configured to vent the exhaust to theatmosphere.

Compressor 134 can be disposed downstream from the supply of oxidant108. The compressor 134 may draw-in and compress the oxidant that isused to drive the cathode ejector 114 and auxiliary ejector 116. In thisexample, compressor 134 is configured to provide the compressed oxidantto recuperator 142.

In some embodiments, the fuel cell system 100 may be one of a pluralityof integrated fuel cell systems. As can be seen on the right hand sideof FIG. 1, the right-pointing arrow beneath the cathode ejector 114 andlabeled as “To Additional Integrated Blocks” indicates that the oxidantmay flow toward another integrated fuel cell system to supply oxidant tothe cathode ejector and auxiliary ejector of that system. In such anembodiment, the compressor 134 may provide compressed oxidant for theplurality of integrated fuel cell systems. Similarly, and as indicatedby the arrow labeled “From Additional Integrated Blocks,” the exhaustfrom auxiliary ejector 116 can be supplied to a common exhaust headerwhich feeds into turbine 136. In some embodiments, multiple turbines andcompressors may be used among the plurality of integrated fuel cellsystems.

FIG. 2 illustrates a fuel cell system 200 that includes similarcomponents as those described above with respect to FIG. 1. Similar tothe fuel cell system 100 of FIG. 1, the system includes IBR of fuel. Forexample, in some examples all fuel reforming occurs in the fuel cellstack 102. In this example, however, fuel cell stack 102 includes twocompartments, namely, a first compartment 103 and a second compartment104. The fuel cell system 200 also includes two anode ejectors includinganode ejector 112 and anode ejector 113, as well as two pre-reformersincluding pre-reformer 144 and pre-reformer 145.

Anode ejector 112 can receive a source of fuel from fuel source 110, andcan also receive fuel exhaust from a fuel exhaust manifold 118 fromcompartment 104 of fuel cell stack 102. The anode ejector 112 isconfigured to supply the fuel to the pre-reformer 144.

The pre-reformer 144 can be disposed between the outlet of anode ejector112 and the fuel supply manifold 120 of compartment 103 of fuel cellstack 102. The pre-reformer 144 functions to remove higher hydrocarbonsfrom the stream of fuel from the outlet of the anode ejector 112, andany higher hydrocarbons that may exist in the fuel exhaust recycled tothe anode ejector 112. The pre-reformer 144 supplies the stream of fuelto the fuel supply manifold 120 of compartment 103 of fuel cell stack102.

Similarly, anode ejector 113 can receive a source of fuel from fuelsource 110, and can also receive fuel exhaust from a fuel exhaustmanifold 128 from compartment 103 of fuel cell stack 102. The anodeejector 113 is configured to supply the fuel to the pre-reformer 145.

The pre-reformer 145 can be disposed between the outlet of anode ejector113 and the fuel supply manifold 130 of compartment 14 of fuel cellstack 102. The pre-reformer 145 functions to remove higher hydrocarbonsfrom the stream of fuel from the outlet of the anode ejector 113, andany higher hydrocarbons that may exist in the fuel exhaust recycled tothe anode ejector 113. The pre-reformer 145 supplies the stream of fuelto the fuel supply manifold 130 of compartment 104 of fuel cell stack102

In some examples fuel source 110 provides desulfurized natural gas toboth anode ejector 112 and anode ejector 113. Methane that may exitanode ejector 112 is converted to synthesis gas in compartment 103 offuel cell stack 102 through steam reforming. The resultant synthesis gasis converted to carbon dioxide and water through the electrochemicalprocess of the fuel cell stack 102. Similarly, all methane that may exitanode ejector 113 is converted to synthesis gas in compartment 104 offuel cell stack 102 through steam reforming. The resultant synthesis gasis converted to carbon dioxide and water through the electrochemicalprocess of the fuel cell stack 102. As such, the use of two anodeejectors in this example allows for the delivery of fuel to fuel cellstack 102 with a lower methane concentration than in some systems thatmay use just one anode ejector. In some examples, the anode ejectorscombine to deliver fuel with a methane concentration of no more than11%.

FIG. 3 illustrates a fuel cell system 300 similar to the fuel cellsystem 200 of FIG. 2, but also includes heat exchanger 306. In thisexample, prior to flowing into the oxidant supply manifold 122 of fuelcell stack 102, the oxidant flows through cold-side channels of heatexchanger 306. In this example, the cathode ejector 114 is configured toreceive fresh oxidant from the source of oxidant 108, and supplies theoxidant to the hot-side channels of heat exchanger 306.

The hot side channels of heat exchanger 306 are supplied with a sourceof hot fluid such as, in this example, the exhaust from auxiliaryejector 116. In other examples, another warm fluid may be used. Forexample, the warm fluid may be combustion products from a combustor thatmay be integrated into the auxiliary ejector 116 and combusts a portionof fuel exhaust from the anodes of the fuel cell stack 102, the oxidantexhaust from the cathodes of the fuel cell stack 102, oxidant from thecompressor 134, or a combination of these fluids. After passing throughthe hot side channels of the heat exchanger 306, the warm fluid can besupplied to the suction side of the auxiliary ejector 116, as in thisexample. In some examples, the warm fluid can be vented out to theenvironment.

FIG. 4 illustrates a fuel cell system 400 that is similar to the fuelcell system 300 of FIG. 3. In this example, however, the heat exchanger306 is downstream, rather than upstream, of cathode ejector 114. Assuch, in this example, the cold-side channels of heat exchanger 306receive oxidant from oxidant supply 108. After passing through heatexchanger 306, the oxidant is provided to cathode ejector 114. As in thefuel cell system 300 of FIG. 3, the hot side channels of heat exchanger306 are supplied with a source of hot fluid such as, in this example,the exhaust from auxiliary ejector 116. After passing through the hotside channels of the heat exchanger 306, the warm fluid can be suppliedto the suction side of the auxiliary ejector 116, as in this example. Insome examples, the warm fluid can be vented out to the environment.

Among other advantages, the present disclosures provide for fuel cellsystems that include fuel cell stacks configured for in-block reforming.The fuel cell systems include pre-reformers where incoming fuel ispre-reformed to remove higher hydrocarbons, and the remainder of thefuel is reformed directly in the fuel cell stack without the need for anexternal reformer. In this manner, the difference between the fuel cellstack (cathode) air temperature at the outlet of the fuel cell stack andthe inlet of the fuel cell stack is significantly reduced. As a result,the temperature of the fuel incoming to the fuel cell stack inlet isincreased. In addition, the temperature of the fuel exiting the fuelcell stack is decreased, thus reducing fuel cell stack exit degradation.Another advantage is a more uniform current distribution within the fuelcell stack, leading to a longer lasting fuel cell stack. There are alsocost advantages to this system, as there is no need for an externalreformer in the fuel cell system. Other advantages of the presentsubject matter will be readily apparent to one skilled in the art towhich the disclosure pertains from a perusal of the claims, the appendeddrawings, and the following detail description of the embodiments.

While preferred embodiments of the present subject matter have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the subject matter is to bedefined solely by the appended claims when accorded a full range ofequivalence, and the many variations and modifications naturallyoccurring to those of skill in the art from a perusal hereof.

We claim:
 1. A method in a fuel cell system comprising: expelling, by afuel exhaust manifold of a fuel cell stack, fuel exhaust; expelling, byan oxidant exhaust manifold of the fuel cell stack, oxidant exhaust;receiving, by an anode ejector, fuel from a source of fuel; receiving,by the anode ejector, a first portion of the fuel exhaust from the fuelexhaust manifold; supplying, by the anode ejector, a stream of fuelcomprising at least a portion of the received fuel and the receivedfirst portion of the fuel exhaust to a pre-reformer; removing, by thepre-reformer, higher hydrocarbons from the stream of fuel from the anodeejector; providing, by the pre-reformer, the stream of fuel to a fuelsupply manifold of the fuel cell stack for in-block reforming;receiving, by an oxidant supply manifold of the fell cell stack, anoxidant from a source of oxidant; and in-block reforming, by the fuelcell stack, of the stream of fuel with the received oxidant, wherein allfuel reforming of the fuel cell system is performed by the fuel cellstack and the pre-former is an adiabatic catalytic converter configuredto remove the higher hydrocarbons with no heat input other than heatfrom the stream of fuel from the anode ejector, wherein the anodeejector includes a first anode ejector and a second anode ejector,wherein the pre-reformer includes a first pre-reformer and a secondpre-reformer, and wherein the first pre-reformer is disposed between anoutlet of the first anode ejector and the fuel supply manifold, and thesecond pre-reformer is disposed between an outlet of the second anodeejector and the fuel supply manifold.
 2. A method in a fuel cell systemcomprising: expelling, by a fuel exhaust manifold of a fuel cell stack,fuel exhaust; expelling, by an oxidant exhaust manifold of the fuel cellstack, oxidant exhaust; receiving, by an anode ejector, fuel from asource of fuel; receiving, by the anode ejector, a first portion of thefuel exhaust from the fuel exhaust manifold; supplying, by the anodeejector, a stream of fuel comprising at least a portion of the receivedfuel and the received first portion of the fuel exhaust to apre-reformer based on a recycle ratio in the range of 4.5 to 15 of amass of the first portion of the fuel exhaust from the fuel exhaustmanifold to a mass of the fuel from the source of fuel; removing, by thepre-reformer, higher hydrocarbons from the stream of fuel from the anodeejector; and providing, by the pre-reformer, the stream of fuel to afuel supply manifold of the fuel cell stack, wherein the pre-former isan adiabatic catalytic converter configured to remove the higherhydrocarbons with no heat input other than heat from the stream of fuelfrom the anode ejector, wherein the anode ejector includes a first anodeejector and a second anode ejector, wherein the pre-reformer includes afirst pre-reformer and a second pre-reformer, and wherein the firstpre-reformer is disposed between an outlet of the first anode ejectorand the fuel supply manifold, and the second pre-reformer is disposedbetween an outlet of the second anode ejector and the fuel supplymanifold.
 3. The method of claim 2 comprising supplying, by the anodeejector, a stream of fuel comprising at least a portion of the receivedfuel and the received first portion of the fuel exhaust to apre-reformer based on a recycle ratio in the range of 6 to 8 of a massof the first portion of the fuel exhaust from the fuel exhaust manifoldto a mass of the fuel from the source of fuel.
 4. A method in a fuelcell system comprising: expelling, by a fuel exhaust manifold of a fuelcell stack, fuel exhaust; expelling, by an oxidant exhaust manifold ofthe fuel cell stack, oxidant exhaust; receiving, by an anode ejector,fuel from a source of fuel; receiving, by the anode ejector, a firstportion of the fuel exhaust from the fuel exhaust manifold; supplying,by the anode ejector, a stream of fuel comprising at least a portion ofthe received fuel and the received first portion of the fuel exhaust toa pre-reformer, wherein a weight percent of methane in the stream offuel supplied by the anode ejector is no greater than eleven percent;removing, by the pre-reformer, higher hydrocarbons from the stream offuel from the anode ejector; and providing, by the pre-reformer, thestream of fuel to a fuel supply manifold of the fuel cell stack, whereinthe pre-former is an adiabatic catalytic converter configured to removethe higher hydrocarbons with no heat input other than heat from thestream of fuel from the anode ejector, wherein the anode ejectorincludes a first anode ejector and a second anode ejector, wherein thepre-reformer includes a first pre-reformer and a second pre-reformer,and wherein the first pre-reformer is disposed between an outlet of thefirst anode ejector and the fuel supply manifold, and the secondpre-reformer is disposed between an outlet of the second anode ejectorand the fuel supply manifold.